On 19 Aug 2012 12:56:24 GMT, AL_n wrote:

Can anyone suggest a logical sequence of things I should check?

In was going to say check the fan/vane/throttle linkages and springs for
correctness and not bent gunked up etc. Note that these linkages quite
often have huge amounts of slack in them a springs that a also slack in
the rest state. Best to get a diagram of the layout rather than guess...

PS... Now when I try to fire it up, it starts up OK, but then dies out
after about one second...

But that sounds like fuel starvation. Is the breather hole in the tank
clear? Does it run with the cap loose? Is the fuel filter clear? Time to
dismantle inspect the tank/carb/gaskets. As it did run well before do not
be tempted to adjust any of the jets or poke anything through orfices.
Backwards washing with clean fuel or a gentle blast of compressed air
should clear any miniscule spots of gunk.

--
Cheers
Dave.